Three-dimensional objects of complex shape can be formed utilizing a computer guided beam of light, typically ultraviolet light such as that from a laser, to polymerize a layer of a liquid, ultraviolet-curable, ethylenically unsaturated material at the surface of a liquid reservoir of such material. The polymerized layer is then coated with additional liquid ethylenically unsaturated material, as for example by lowering that layer into the reservoir, and the light is again utilized to polymerize the layer of ethylenically unsaturated material at the surface of the reservoir to produce another polymerized layer which adheres to the layer beneath it. These steps of coating and polymerizing superimposed layers of ethylenically unsaturated material which adhere to one another are repeated to produce a three-dimensional object. This process is well known in the prior art, e.g., U.S. Pat. No. 4,575,330 to Hull, and is known as "stereolithography".
The ethylenically unsaturated material conventionally includes acrylate and/or methacrylate constituents. These constituents are odorous, hazardous and costly. Therefore, special care must be taken in handling, storing, and disposing of these materials.
The reservoir used in the above process must be of sufficient size to accommodate the largest dimension of the object being formed, because the completed object is positioned entirely within the reservoir. Large objects thus require large reservoirs that contain large amounts of potentially hazardous ethylenically unsaturated material.
FIG. 4 of the Hull Patent, and the accompanying disclosure at column 9, line 46 to column 10, line 5, teaches floating the ultraviolet-curable liquid 22 on a heavier, ultraviolet transparent liquid layer 32. The ultraviolet light source 26 passes through the ultraviolet transparent liquid layer 32 and is focused at the interface between the ultraviolet-curable liquid 22 and the ultraviolet transparent liquid layer 32. As a result the object 30 is pulled up out of the ultraviolet-curable liquid 22 as it is formed. Hull asserts that a smaller volume of ultraviolet-curable liquid 22 is required since part of the object being formed can be raised out of the ultraviolet-curable liquid 22.
Although this procedure of Hull may be applicable to smaller objects, larger and heavier objects could be pulled off the support, or stretched to deform the object, due to their own weight. Hull's approach is therefore of limited value for the production of larger and heavier objects. No reduction in the volume of ultraviolet-curable liquid 22 is achieved if the volume of ultraviolet-curable liquid 22 is sufficient to contain, and thereby partially bear the weight of, the entire object to minimize the weight tending to pull the object from its support. In contrast, the present invention permits a reduction in volume of radiation-polymerizable liquid material, e.g., an ethylenically unsaturated material, while containing the entire object.
The Hull Patent does not suggest inhibiting the contacting of these two liquids 22 and 32, so there is nothing to prevent undesired interaction between these two liquids which can adversely effect the cure of the ultraviolet-curable liquid 22. However, the present invention inhibits interaction by separating the two phases.
Furthermore, the reservoir can become contaminated and unstable with use and with the passage of time. A larger reservoir increases the amount of waste of expensive material that can result from contamination and instability, and it also increases the disposal problem. The chemical instability of the material in the reservoir can result in an uncontrolled, exothermic polymerization. This can result in damage to equipment and it can even be explosive. The larger the quantity of hazardous material in the reservoir, the greater the problem. The present invention reduces the quantity of hazardous material present and thereby reduces the problem.